问题
I am plotting a pandas dataframe with a second y-axis via pandas plotting interface as described in the documentation like this:
df = pd.DataFrame(np.random.randn(24*3, 3),
index=pd.date_range('1/1/2019', periods=24*3, freq='h'))
df.columns = ['A (left)', 'B (right)', 'C (right)']
ax = df.plot(secondary_y=['B (right)', 'C (right)'], mark_right=False)
ax.set_ylabel('A scale')
ax.right_ax.set_ylabel('BC scale')
ax.legend(loc='upper right')
plt.show()
which yields
As it can be seen, the legend looses entries when I set the position using ax.legend(loc='upper right').
Does anyone know how I can set the legend position and keep all entries?
Thanks in advance!
回答1:
We can use .get_legend_handles_labels() for a more correct solution:
np.random.seed(42)
df = pd.DataFrame(np.random.randn(24*3, 3),
index=pd.date_range('1/1/2019', periods=24*3, freq='h'))
df.columns = ['A (left)', 'B (right)', 'C (right)']
ax = df.plot(secondary_y=['B (right)', 'C (right)'], mark_right=False)
ax.set_ylabel('A scale')
ax.right_ax.set_ylabel('BC scale')
h1, l1 = ax.get_legend_handles_labels()
h2, l2 = ax.right_ax.get_legend_handles_labels()
ax.legend(h1+h2, l1+l2, loc=1)
The reason we need to use that method is because ax and ax.right_ax each have their own legend and simply setting them to the same location will render them on top of each other.
来源：https://stackoverflow.com/questions/54090983/set-legend-position-when-plotting-a-pandas-dataframe-with-a-second-y-axis-via-pa